Allotter circuit for sequential indication of incoming telephone calls

ABSTRACT

A telephone call allotter circuit is disclosed for lighting the line lamps on an attendant console or switchboard, one at a time, in the same sequence in which calls arrive. A crossbar switch is interposed between the line relays and the line lamps. The horizontal magnets of the switch are operated sequentially in the order in which calls arrive. The line lamp of each line is associated with a respective vertical of the crossbar switch. Transfer contacts of relays controlled by the crossbar switch permit only one line lamp at a time to operate.

United States Patent INDICATION OF INCOMING TELEPHONE CALLS 7 Claims, 8Drawing Figs.

[56] References Cited UNlTED STATES PATENTS 2,546,647 3/1951 Marble etal 179/94 Primary Examiner-William C. Cooper Assistant Examiner-ThomasW. Brown Attorneys-N. S. Ewing and James Warren Falk ABSTRACT: Atelephone call allotter circuit is disclosed for lighting the line lampson an attendant console or switchboard, one at a time, in the samesequence in which calls arrive. A crossbar switch is interposed betweenthe line relays and the line lamps. The horizontal magnets of the US. Cl179/27, switch are operated sequentially in the order in which calls ar-179/94 rive. The line lamp of each line is associated with a respectivelnt.Cl H04m 5/04 vertical of the crossbar switch. Transfer contacts ofrelays Field of Search 179/27 controlled by the crossbar switch permitonly one line lamp at (CI), 27.1, 27.02, 27.25, 84L (Cursory), 94 atimeto operate.

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)-l WP K PI I r 75517 75A'I7 ZSTAIQ I a I I acc ZSTBO I H5 I I 1 IL I H9G1 :1 I SBIS 7SB|7 I 75517 l, j l 25KB] VQ v19 P|7 I SHMO 2SITB0 5SM25SMI 5SMO I I I l v V -2srB|9' zsc 15m SAI|\ SA5\' 5HMI ZSITBI u 7SAI75W5 SA13 SAl2 SWITCH 5 0-4 0-1 I CONTROL l 5HM19 ZSTBIQ CIRCUIT SA5 i Al6SAO\ zcc I 500 U PATENTED m 419?! SHEET 3 [IF 7 I ll'lll l m; N QFENmen an ALLO'I'I'EHR CIRCUIT FOR SEQUENTIAL INDICATION F DICOMINGTELEPHONE CALLS BACKGROUND OF THE INVENTION This invention relates totelephone call allotter circuits and, more particularly, to circuits forindicating to an attendant at an answering position which of a pluralityof incoming calls should be answered next.

When a plurality of incoming calls appear at an attendant position andare not immediately answered because all of the attendants are busy,either busy tone must be returned to the calling line or the unansweredcalling lines must be held in abeyance until an idle attendant isavailable. In many installations such as at mail order sales desks,airline reservation desks, etc., it is commercially disadvantageous toreturn busy tone to a calling party and, accordingly, telephoneequipment is provided which automatically holds these incoming callsuntil they can be answered by an attendant. The presence of a call whichis waiting to be answered is usually indicated by an illuminated linelamp. In a large installation having a great number of incoming linesthe lighting of the line lamps corresponding to all of the calling linesawaiting answer would create a confusing display for an attendant.

Heretofore, some semblance of order has been maintained at theattendants position by one of two methods. Either one incoming line at atime is automatically connected to an attendant's position by theallotter circuitry, or all incoming lines are connected through to theattendants position but only one line lamp at a time is lighted undercontrol of the allotter. Both the routing of one call at a time and thelighting of one lamp at a time are accomplished in part by a lockoutcircuit. Any lockout circuit has an inherent priority due to its wiringconfiguration. This inherent priority created a distinct problem in theprior art arrangements. For example, if an attendant were busy while twoincoming calls arrived, the next call routed to the attendant might notbe the first to arrive but would bethe one arriving over the higherpriority line. When trafiic to the attendant position was light, thiscreated no particular problem since the other call would be answeredshortly, even though not in the sequence of its arrival. However, whencalling trafiic is heavy, so that a number of calls are beingheld andnew calls are arriving as fast as held calls are answered, it 'ispossible for a call to arrive over a low priority line and wait aninordinate time to be answered. Under these heavy traffic conditionswhen a number of calls are being held and new calls continue to arriveit is to be expected that whenever the attendant becomes idle a higherpriority call will always be waiting and will preempt the low prioritycall, eventually causing the low priority caller to lose patience andabandon the call.

It is therefore an object of this invention to provide a telephone callallotter circuit capable of registering the sequence of arrival of aplurality of calls at an attendant position and then displaying eachcall to the attendant in the exact sequence of its arrival.

SUMMARY OF THE INVENTION The foregoing and other objects of my inventionare achieved, in one illustrative embodiment, by providing a telephonecall allotter circuit employing a crossbar switch having its verticalsindividually associated with the incoming lines and having itshorizontals operated sequentially in the order in which calls arrive.The crossbar switch is arranged so that one of its crosspoints is closedas each call arrives, the

tal levelsdictated by their precedence of arrival. The switch 7accordingly stores" the calls on its crosspoints until answered and, aseach call is answered, provides the operating path for illuminating thenext call s line lamp.

When an attendant answers one of the calls, the operated crosspointassociated with that call is released. This enables an operating path tobe completed to the line lamp of the calling line which had operated itscrosspoint immediately succeeding the operation of the crosspoint justreleased. Calls that arrive after the aforementioned crosspoint has beenreleased are not permitted to operate any crosspoint on the horizontallevel of this just-released crosspoint until crosspoints associated withall subsequent horizontal levels of the crossbar switch have beenoperated. In this manner a later arriving call is prevented fromoperating a crosspoint that should only be associated with an earlierarriving call. When all'of the horizontal levels have finally beenselected and the attendant has answered the 4 BRIEF DESCRIPTION OF THEDRAWING The foregoing and other objects of the invention may be morereadily comprehended from an examination of the following specification,the appended claims and drawings in which:

FIG. 1 shows an overall block diagram of a specific illustrativeembodiment of the invention, the details of which are shownin FIGS. 2-7;

2 shows the start circuit which is responsive to operation of the linerelays of the calling lines;

FIG. 3 shows the line lamps together with the upper two levels of thecrossbar switch;

FIG. 4 shows the lower levels of the crossbar switch;

FIG. 5 shows a switch control circuit which includes the select and holdmagnets for the crossbar switch;

FIGS. 6 and 7 show the sequence allotter circuit; and

FIG. 8 shows the appropriate arrangement of 'FIGS. 3 through 7.

GENERAL DESCRIPTION Referring now to FIG. 1, there is shown, inabbreviated schematic form, a telephone call allotter circuit 160 whichmay be associated with an attendant switchboard (not shown) so that aplurality of calls, arriving at the attendant switchboard 'over theplurality of incoming lines 0 through 19 from a central offioe switchingnetwork 120, may light the respective line lamps L0 through L19 ondisplay panel 300 one at a time in the same sequence as the one in whichthe callsarrive. The operating paths for the lamps are prepared bycrossbar switching network 400 operating under control of switch controlcircuit 500. The 'tip and ring leads associated with the incoming linesdo not appear at the call allotter circuit and may be switched directlythrough the central office switching network to the attendantswitchboard in the conventional manner. Of course, as'will be apparentto those skilled in the art, the tip and ring could be switched throughnetwork 400 if more wires per crosspoint were utilized than are depicted.in the illustrative embodiment. To simplify the presentation however itwill be assumed that network 400 does not switch'the tip and ringconductors of the lines.

Each vertical of network 400 is associated with .a particular incomingline and line lamp. The horizontal levels are associated with the orderof call arrival. An incoming call operates its respective one of linerelays 2STAO through ZSTA'I'Q in start circuit 200. The operated linerelay.,in turn, operatest'he associated relay 28130 through 28118l9,.also'in start circuit 200. The operation of any ZSTB- relay causesrelay ZCC instart circuit 200 to operate. With relay 2CC operated, apath is completed in switch control circuit 500 to operate particularselect magnets, one from the group 5SMO through SSM2, and one from thegroup 5SM4 through 5SM9.

The select magnets operate in a predetermined sequence through variouscontacts of relays 6SAO through 6SAI7 in the allotter sequence controlcircuit 600. The operation of the select magnets operates the 28C relaywhose winding is not shown in FIG. 1 but one of whose contacts, inswitch control circuit 500, completes the operating path for the holdmagnet 5I-IMO through SHMW associated with the incoming line in controlcircuit 500. The operating of a horizontal and vertical magnet completesa path through crossbar switching network 400 to operate one relay ofthe group 6830 through 78317 in control circuit 600. For example, withcrosspoints closed at vertical level V0 and horizontal levels H0 and H4,a path is completed from ground, through a make contact ZSTAO,crosspoint V0/l-I0, crosspoint Vtl/H, via pair P0 to circuit 600, andthrough a break contact 6881 to operate relay 6580.

This in turn completes an operating path from ground in circuit 600,through a make contact 6880, a break contact 78817, via pair P0 tonetwork 400, crosspoint Vii/H4, and crosspoint VO/HO, to lamp L0 indisplay panel 300.

As each crosspoint connection is made in network 400, the relays incircuit 600 operate in sequence, one for each incoming call. Theoperation of a 685- relay in circuit causes its associated 6SA- relay tooperate, thereby preparing the operating paths for the next pair ofselect magiets to operate sequentially in control circuit 50%).Operation of the 688- relay also partially completes a path, as will beexplained later in more detail, through network 400 to operate the lampL0 through L19, on display panel 300, associated with the next call insequence to be answered. When one call is answered, its associated 6313-relay releases, which completes the operating path for the lampassociated with the next call to be answered. This too will be explainedin detail hereafter.

In the illustrative embodiment, a 2-wire path is required for allottinga sequence position to each arriving call. A conventional lo-horizontallevel, 6-wire crossbar switch is employed so that the -wire crosspointsmay serve three lines. In this manner, I8 effective horizontal levelsare obtained and 18 sequence positions may be stored.-

DETAILED. DESCRIPTION In the following detailed description it will beassumed that a first call is received on line 2 and storedon acrosspoint of network 400. Next a call will be received on line 0 and ittoo will be registered at a crosspoint with neither the first nor secondcall being immediately answered. Then a third call will be received online 19 and it too will be held while none of the preceding calls isanswered. At this point the first call, on line 2, will be answered.Thereafter it will be assumed that a number of calls continue to arrivewithout being answered until a call is received on line 1, which callwill represent the last call which can be stored in network 400.

Arrival of First Call Asuming now that the first call in an illustrativesequence of incoming calls arrives on line 2, its line relay or othercall detecting device (not shown) will in any conventional mannercomplete an operating path to line relay 2STA2 in start circuit 200,FIG. 2. In the following description all relays and magnets, such asrelay 2ST A2, are designated by an alpha-numerical code in which theleftmost number of the designation indicates the FIG. of the drawing inwhich the winding appears. Each contact of a relay or magiet isindividually numbered, the contact number being g'ven after the dash.Thus, the designation 2STA2-l in the center of FIG. 2 indicates a first(make) contact of relay 2STA2. The winding of this relay is found at theleft center of FIG. 2. All potential sources not otherwise marked areassumed to be 48 volts.

Relay 2STA2 having been operated, an operating path for relay 2STB2 iscompleted, which path may be traced from the winding of relay 2STB2through break contact 5I'IM2-2'of hold magnet SI-IMZ, diode 212, makecontact 2STA2-l and break contacts 2SC-1 and 2CC-l to ground. Uponoperating, relay 2STB2 locks operated to ground through the make portionof its own transfer contacts 2STB2-1 and the break portion of thetransfer contacts of relays 2STB3 through 2STB19, relays 2STB3 through2STB18 being represented by the dotted line. Relay 2STB2 operated at itsmake contact 2STB2-2 completes an operating path for relay 2CC whichoperates and at its break contact 2CC-1 interrupts the originaloperating path for relay 2STB2 (and all other 2STB- relays, as well).Relay 2STB2 does not release due to the previously established holdingpath.

In operating, relay 2CC also completes operating paths for selectmagnets SSMO and 5SM4 in the switch control circuit 500 of FIG. 5.Select magnet 5SMO operates over path including the break portion oftransfer contacts SAS-4, break contact 6ESA-3 and make contact 2CC-3 toground. The aforementioned contacts SA5-4 are not preceded by anumerical designation inasmuch as the winding of the SAS relay is notshown in any FIG. of the drawing. Relay SAS is one'of the series of 18similarly wired SA relays of which the first three are shown in FIG. 6and the last is shown in FIG. 7. The operating path for select magnet5SM4 includes the break portion of transfer contacts 6SAO-3, lead 505 toFIG. 7, break contact 6ESA-2 and the make portion of transfer contacts2CC-2 to ground.

Operation of select magnet 5SMO selects the uppermost horizontal levelof contacts designated H0 of the crossbar switching network 400 in FIG.3. Operation of select magnet SSM l selects the horizontal leveldesignated H4 in FIG. 4. The operation of select magnets 5SMO and 5SM4at their respective contacts SSMO-I and 5SM4-l in FIG. 2 completes thepath for relay 28C to operate.

Relay 2SC operated at its make contact 2SC-2 in FIG. 5 completes anoperating path for hold magnet 5I-IM2 through previously operated makecontact 2STB-3. Upon operating, hold magnet 5I-IM2 locks operatedthrough its own make contact and make contact 2STA2-2 to ground. Theoperation of hold magnet 5HM2, with select magnets 58M!) and 5SM4operated, closes crosspoints of vertical V2 at horizontal levels H0 andH4 and completes the operating path for the first posi tion of sequenceallotter circuit 609. This path may be traced from ground in FIG. 3,through make contact 2STA2-2, crosspoints 351 and vertical V2 tocrosspoints 451, at horizontal level H4 in FIG. 4, lead S0 of lead pairP0 to FIG. 6, diode 710, the break portion of transfer contacts 6SBl-2to the winding of relay 6830. Relay 6SBO operates and locks to lead S0through its make contact 68130-1. Relay 65B!) operated completes a pathfor lighting line lamp L2 on display panel 300, which path may be tracedfrom ground in FIG. 6, through the make portion of transfer contacts6880-3, the break portion of transfer contacts 7SB17-4 to lead LLO oflead pair P0 at horizontal level H4, through crosspoints 452 and 352 atvertical V2 to lamp L2 in FIG. 3. Lamp L2 lights to indicate that line 2has an incoming call, and that that call presently has the longestwaiting time. It should be noted that this path was completed over abreak contact of released relay 78817 which relay, as hereinafter to bedescribed, would only be operated if there had been 17 previouslyunanswered calls stored at crosspoints in network 400.

When hold magnet 5I-IM2 operates to close the crosspoints, its breakcontact 5I-IM2-2 in FIG. 2 opens the hold path for relay 2STB2 whichreleases. The release of relay 2STB2 at its released make contact2STB2-2, causes relay ZCC to release, which, at its released makecontacts 2CC-3 in FIG. 5 and 2CC-2 in FIG. 7, releases the operatedselect magnets SSMt) and 5SM4. The release of the select magnets,SSMll-l and 5SM4-l contacts in FIG. 2, opens the operate path of relay2SC. Relay 28C released interrupts the operating path for all of thehold magnets in FIG. 5 except hold magnet SHMZ which by its locking pathis held operated so long as line 2 maintains relay 2STA2'operated.

The release of relay 2CC, at its released break contact ZCC-Z in FIG. 7,completes an operating path through operated make contacts6SBO-5 for therelay 6SAO ir FIG. 6. Relay 68M) locks operated through diode 610, itsown make contact 6SAO-l and break contact 6ESA-l to ground. Diode 710 isprovided to isolate the winding of relay 6580 from the groundingprovided over contact tSSAll-l so that relay 6SBO maybe held operatedonly through the ground provided over the closed crosspoints of network400. Accordingly, relay 6SBO remains operated so long as a call ispresent on line 2. The circuit is now ready to allot a position to thenext incoming call.

Arrival of Second Call Assuming that the next incoming'call arrives overline 0, the associated line relay 2STAO will be operated. Since relay2SC has released, the operating path for the 2STBO relay is I completedthrough break contact 5HMO-2, diode210, make make contact of itstransfer contacts 2CC-2 in FIG. 7, applies operating ground throughbreak contact 6ESA-2 toFIG. S via lead 505. Ground on lead 505 isapplied over the make portion of transfer contacts 6SAO-3 and the breakportion of transfer contacts 6SAl-3 to select magnet SSMS. Operation ofselect magnets'SSMO and SSMSat their respectivecontacts SSMtl-I andSSMS-l in FIG. 2 completes an operating path for relay 28C. Relay 28Coperated at its make contacts ZSC-Z in FIG. 5 completes an operatingpath for hold magnet 5HMO through make contact 2STBO-3. Hold magnetSl-IMO locks operated through its own make contact and make contact2STAO-2 togrourid. I

, The operation of hold magnet Sl-IMO at its break contact 5HMO-2 inFIG. 2 opens the holding path 'for relay ZSTBI), which releases,releasingrelay 2CC. The release of relay 2CC releases select magnetsSSMO and 5SM5, which release relay 28C.

. The closure of crosspoints of vertical V at levels H0, FIG. 3, andlevel H5, FIG. 4, completes an operating path for relay 6881 in FIG. 6which may be traced from ground in FIG. 3 through make contact ZSTAfl-Z,closed crosspoints 3 61 and vertical Vt) to crosspoints 461 in FIG. 4,lead S1 of lead pair P1 to FIG. 6, through diode 711, andthe breakportion of transfer contacts 6832-2 to the winding of relay 6581. Onoperating, relay 688i. locks to lead S1 through its own make contact6531-1. The operating path for the L0 lamp on display panel 3% ispartially completed through network 400 at closed crosspoints 362 and462, to lead LLI in FIG. 6 where it is interrupted by the break portionof transfer contacts 6880-4. Relay 6580 was operated by the first calland will remain operated until that call is answered. Relay 6SB1operated, operates relay 6SAR through make contact 6581-5 and the breakportion of transfer contacts ZCC-2 to ground 'in ,FIG. 7. Relay 6SA1then locks operated through'diode 611, its own make contact ,fiSAl-I andbreak contact tiESA-l to ground. Diode 711 isolates the S1 lead from thelocking path of relay 6SA1 so that relay 6881 is locked operated onlythrough network via lead S1. Hold magnet SHMO and relays 68B] and 6SA1are held operated through their established holding paths.

Arrival of Third Call 2STB19 over a path including break contact5HMl9-2, diode 229, make contact 2STA19-1and break contacts 2SC-l and2CC-1 to ground. Relay *2STB19 locks operated through the break contact5HMl9-2 of bold magnet 5HM19 and the make portion of its own transfercontacts 2STB19-1 to ground. As before, relay 2CC operates and completesthe operating path for a pair of select magnets in FIG. 5. Select magnet5SMO operates as it did previously, while select magnet 5SM6 operatesthrough the break portion of transfer contacts 6SA2-3, the make portionof transfer contacts 6SAI-3 and 6SAO-3, over lead 505 to FIG. 7, throughbreak contact 6ESA-2 and the make portion of transfer contacts 2CC-2 toground Relay 2SC operates over an obvious path and, in FIG. 5, completesthe operating path for hold magnet 5HM19 in series with operated makecontact 5STB19-3. Hold magnet 5HM19 operated locks operated through itsown make contact and make contact 2STA19-2 to ground. In a mannersimilar to that previously described, the 6532 relay operates throughclosed crosspoints 371 and 471 and the operating path for lamp L19 iscompleted through network 400 via crosspoints 372 and 472 to lead S2,where it is interrupted by the break portion of transfer contacts'6SBl-4. Relay 6SA2 operates through the make contact 6SB2-5 and themake portion of transfer contacts 2CC-2 to ground. It then locksoperated .through diode 612, its own make contact and break contact6ESA-1 to ground. Diode 712 isolates the S2 lead from the above lockingpath so that relay 6882 is locked operated onlythrough network 400 vialead S2. In operating, hold magnet SHM19 also precipitates the releaseof the position allotting portion of the circuit, as previouslydescribed. Hold magnet 5HM19, and relays 6SB2 and'6SA2 are held operatedthrough their respective holding paths.

Call Answered by Attendant L2, associated with incoming line 2, overwhich the first call arrived, is still lighted. When the attendantbecomes available and answers the call on line 2 she does so byoperating a pickup key whose break contact PUZ opens the operatingpathfor line relay 2STA2. The release of relay 2STA2 at its releasedmake contact 2STA2-2, in FIG. 3, removes ground from crosspoints 351 and451 and interrupts the S0 lead holding path for relay 6830 in FIG. 6which relay also releases. The release of relay 6380 interrupts the LLI)lead operating path for lamp L2 in FIG. 3 and lamp L2 is extinguished.At the same time, the operating path for lamp L0 which was partiallycompleted by the operation of crosspoints 362 and 462 when the secondcall arrived over line 0 is now completed to lead LLl in FIG. 6 over thebreak portion of transfer contacts 6850-4 and the make portion oftransfer contacts 6881-3 to ground. Lamp L0 now operates to indicatethat line 0 has the next call in sequence.

Arrival of the Eighteenth Call Let it be assumed that the eighteenthcall arrives over line 1. Relays ZSTAI and ZSTBI in FIG. 2 operate inthe manner previously described. Select magnets SSMZand 5SM9 in FIG. 5operate when make contacts 2CC-2 and 2CC-3 operate. The path for selectmagnet 5SM2 includes the breakportion of transfer contacts 7SAl7-4, themake portions of transfer contacts 8A1 1-4 and SAS-d, break contact6ESA-3 and make contact 2;CC -3 to ground. Select magnet 5SM9 operatesIn operating, hold magnet SHMI opens both the operating and holdingpaths for relay 2STB1 at its break contact Sl-IMl-Z in FIG. 2. Therelease of relay 2STB1 initiates the release of relay ZCC, selectmagnets SM2 and 5SM9, and relay 28C.

The operation of hold magnet SHMl also results in the closure ofcrosspoints on vertical V1 at horizontal levels H2 and H9. Thiscompletes an operating path for relay 78817 which may be traced fromground in FIG. 3 through make contact 2STAl-2, closed crosspoints 391and vertical V1 to closed crosspoints 491 in FIG. 4, lead S17 of leadpair P17 to FIG. 7, through -diode 727, the break portion of transfercontacts 6SBO-2 to the winding of relay 7SBI7. Relay 7SB17 operated,locks to lead S17 through its own make contact 78317-1. The operatingpath for lamp Ll on display panel 300 is partially completed, throughnetwork 400 at closed crosspoints 392 and 492, to lead LL17 where it isinterrupted by the break portion of transfer contacts 8816-4. Relay7SA17 is also operated through make contact 7SB17-5 and the breakportion of transfer contacts 2CC-2 to ground and then locks operatedthrough diode 627, its own make contact and break contact 6ESA-1 toground in FIG. 6. Diode 727 isolates the S17 lead from the locking pathfor relay 7SA17. This insures that relay 78817 is held operated only vialead S17 through network 400.

The allotting of the eighteenth position initiates an end-ofsequenceoperation. The operating path for the 7138 relay has been partiallycompleted from its winding, via lead 525 to FIG. 5, through two parallelpaths. The first includes the make portions of transfer pairs 7SA17-4,SAl 1-4 and SAS-d, and through break contact 6ESA-3 to the unoperatedmake contact 2CC-3. The second path includes the make portions oftransfer pairs 7SA17-3 through 6SAO-3, to FIG. 7 via lead 505, andthrough break contact 6ESA-2 to the unoperated make portion of transferpair 2CC-2. The arrival'of the next call (nineteenth) will cause relayZCC to operate once again, completing these parallel operating paths forrelay 7ES through make contacts 2CC-2 and 2CC3 to ground. The operationof relay 7E8 completes an obvious path for the operation of relay 6ESAin FIG. 6. The operation of relay 6ESA interrupts the operating path forthe 7E8 relay by opening its break contact 6ESA-3 in FIG. 5.

If none of the previously allotted calls have been answered, relay 7158would release and cause busy tone to be returned to the calling party(through means not shown). If, on the other hand, one or more calls havebeen answered so that earlier assigned allotter positions are once moreavailable, relay 7135 would be held operated through a supplementarypath. For example, in the sequence described above, the first call,received over line 2, has been answered. Its associated relays 2STA2 and2STB2 have released, as has the 6830 relay associated with its allottedposition. Relay 6SAO, however, was held operated over its locking paththrough diode 610, its own make contact and break contact 6ESA-l toground. Therefore, a supplementary holding path for relay 758 iscompleted from-its winding, through its own make contact 7ES-3 to FIG.6, through make contact 6SAO-2, and through the break portion oftransfer contact 68130-3 to ground.

The operation of relays 7128 and 6ESA serve to release the I allotterpositions assigned to previously answered calls. The

holding path for the SA- relays is interrupted at break contact 6ESA-lin FIG. 6. At the same time, a supplementary locking path is completedin FIG. 6 through make contact 7ES-2 to ground. However, instead ofholding operated all the previously operated SA- relays, thissupplementary path holds only those SA- relays whose associated SB-relays are also operated (those associated with unanswered calls). Inthe sequence detailed above, relay 6SAO should now release since itssupplementary path is interrupted at make contact 6SBO-5. If diode 610were not present, relay 68M) would not release when the holding paththrough contact 6ESA-1 to ground was interrupted. Instead, anadditional, unwanted holding path would be present through its own makecontact 6SAO-1,

make contacts 6SA1-2 and 6SB1-5 (both relays 68A! and 6881 are stilloperated, since the call at allotter position 1 is unanswered), andthrough make contact 7ES-2 to ground. Diodes 610 through 627 are presentto prevent this unintended holding path from being established. Theremaining SA- relays are held operated through make'contacts 6SB1-5through 7SBl7-5 since relays 68131 through 7SB17 are still operated. Thefirst allotter position would be cleared, however, permitting itsreallotment on the nineteenth call.

Abandoned Calls Assume now that after being allotted position 1 andwhile lamp L2 is still lighted, the call placed over line 0 issubsequently abandoned. The 2STAO relay, hold magnet SHMO andcrosspoints 361, 362 and 461, 462 would all release. If relay 6881 werepermitted to release, the operating path for lamp L19 would be completedfrom the LL2 lead through the break portion of transfer contacts 6881-4and make portion of transfer contacts 6SB2-3 to ground. This would beundesirable since two lamps would now light on display panel 300ratherthan only one as desired. Instead of permitting the SB- relay torelease when the call allotted to a previous position has not beenanswered, the circuit holds that relay operated over a supplementalpath. In the immediate case, the 6SB1 relay is held operated through themake portion of transfer contacts 68804 and the make portion of its owntransfer to ground. This insures the lighting of the line lamps inproper sequence, as well as insuring that only one lamp on display panel300 will be lighted at one time. Subsequently, when the call on line 2is answered, not only will the 6SBO relay release as described above,but the 6881 relay associated with the abandoned call will also release.The line lamp associated with position 2 (L19) will then be lighted, asit becomes the next call in sequence to be answered.

It is to be understood that the embodiment just described isillustrative of the principles of my invention. Other arrangements maybe devised by those skilled in the art which do not depart from thespirit and scope of this invention. For example, while the illustrativeembodiment described the operation of a crossbar switching network,other coordinate-type switching arrays could be employed instead.

Iclaim:

1. A display lamp control circuit for a plurality of line lamps eachassociated with a telephone line, comprising a coordinate switchingarray having a plurality of interconnectable horizontal and verticalconductor paths, said line lamps each being associated with a respectiveone of said vertical paths;

means responsive to a call from one said associated telephone line forautomatically interconnecting one of said horizontal conductor pathswith the vertical conductor path associated with the line lampassociated with said calling line;

first circuit means operable upon the interconnection in said array ofsaid one horizontal and said one vertical conductor paths for preparingan operating path to another of said horizontal paths immediatelysucceeding said one horizontal path; and

second circuit means connected to said horizontal conductor paths forcontrolling said first circuit means and operable in response to theanswering of said call from said calling line for completing anoperating path to the one of said line lamps associated with thevertical path of an interconnection in said array which includes saidimmediately succeeding horizontal path.

2. A display lamp control circuit in accordance with claim I, whereinsaid coordinate switching array comprises a crossbar switch,

and wherein each of said horizontal conductor paths comprises a firstand a second conductor,

said first circuit means includes relay means connected to said firstconductor, and

said second circuit means includes said second conductor and meanscontrolled by said relay means connected to said first conductor of saidone horizontal path for operating said line lamp over said completedpath.

3. A display lamp control circuit for a telephone call allotter circuitincluding a plurality of telephone lines each having a line lampassociated therewith;

a crossbar switch having a plurality of horizontal and verticalconductor paths and horizontal and vertical magnets operable toestablish a plurality of interconnections between said horizontal andvertical paths, said vertical conductor paths being associated withrespective ones of said lines;

and means for lighting one at a time the line lamps associated withcalling ones of said lines comprising:

means connected to said horizontal conductor paths for selectivelyoperating successive ones of said horizontal magnets of said switch; a

means responsive to each operation of one of said horizontal magnets foroperating the one of said plurality of vertical magnets corresponding toa calling one of said lines;

and means operative when one said interconnection established throughsaid switch is released for completing the operating path to one of saidplurality of line lamps and for opening the operating path to another ofsaid line lamps associated with said telephone lines.

4. A display lamp control circuit in accordance with claim 3, whereinsaid means for selectively operating said horizontal magnets comprises aplurality of relays equal in number to said horizontal magnets andoperable sequentially, each of said relays being operable to preventreoperation of an associated one of saidhorizontal magnets when theinterconnection established by said associated one of said horizontalmagnets is released.

5. A display lamp control circuit in accordance with claim 4, furthercomprising means responsive to the release of the interconnectionestablished by the last operable one of said horizontal I magnets forreleasing all of said plurality of relays. 6. A sequential controlcircuit comprising a plurality of lines capable of exhibiting servicerequests, a coordinate switching array having a plurality of horizontallines, said display means having its operating path prepared by acrosspoint connection between its corresponding vertical path and asequentially selected one of said horizontal paths,

means controlled by the crosspoint connection established to the firstof said sequentially selected horizontal paths for completing theoperating path for one of said display means, and I means controlled bythe release of said last-mentioned crosspoint connection for completingthe display device operating path prepared by the next sequentiallyselected one of said horizontal paths.

7. A telephone call allotter circuit comprising a plurality of telephonelines each having a line lamp associated therewith;

a line relay associated with each of said lines, said relay beingoperable in response to the arrival of a call over a respective one ofsaid lines;

a coordinate switching array having a number of horizontal paths equalto the maximum number of calls desired to be held without being answeredand a number of vertical conductor paths equal to the number of saidtelephone lines;

means responsive to the operation of each of said line relays forselecting one of said horizontal paths dependent upon the number of saidhorizontal paths which have previously been selected;

means for completing a crosspoint connection in said array at theintersection of said selected one of said horizontal paths with the oneof said vertical paths corresponding to said respective one of saidlines, each said crosspoint connection being effective to prepare anoperating path to the line lamp associated with a respective calling oneof said plurality of lines; and

means responsive to the release of one of said line relays forcompleting one of said prepared line lamp operating paths.

1. A display lamp control circuit for a plurality of line lamps eachassociated with a telephone line, comprising a coordinate switchingarray having a plurality of interconnectable horizontal and verticalconductor paths, said line lamps each being associated with a respectiveone of said vertical paths; means responsive to a call from one saidassociated telephone line for automatically interconnecting one of saidhorizontal conductor paths with the vertical conductor path associatedwith the line lamp associated with said calling line; first circuitmeans operable upon the interconnection in said array of said onehorizontal and said one vertical conductor paths for preparing anoperating path to another of said horizontal paths immediatelysucceeding said one horizontal path; and second circuit means connectedto said horizontal conductor paths for controlling said first circuitmeans and operable in response to the answering of said call from saidcalling line for completing an operating path to the one of said linelamps associated with the vertical path of an interconnection in saidarray which includes said immediately succeeding horizontal path.
 2. Adisplay lamp control circuit in accordance with claim 1, wherein saidcoordinate switching array comprises a crossbar switch, and wherein eachof said horizontal conductor paths comprises a first and a secondconductor, said first circuit means includes relay means connected tosaid first conductor, and said second circuit means includes said secondconductor and means controlled by said relay means connected to saidfirst conductor of said one horizontal path for operating said line lampover said completed path.
 3. A display lamp control circuit for atelephone call allotter circuit including a plurality of telephone lineseach having a line lamp associated therewith; a crossbar switch having aplurality of horizontal and vertical conductor paths and horizontal andvertical magnets operable to establish a plurality of interconnectionsbetween said horizontal and vertical paths, said vertical conductorpaths being associated with respective ones of said lines; and means forlighting one at a time the line lamps associated with calling ones ofsaid lines comprising: means connected to said horizontal conductorpaths for selectively operating successive ones of said horizontalmagnets of said switch; means responsive to each operation of one ofsaid horizontal magnets for operating the one of said plurality ofvertical magnets corresponding to a calling one of said lines; and meansoperative when one said interconnection established through said switchis released for completing the operating path to one of said pluralityof line lamps and for opening the operating path to another of said linelamps assocIated with said telephone lines.
 4. A display lamp controlcircuit in accordance with claim 3, wherein said means for selectivelyoperating said horizontal magnets comprises a plurality of relays equalin number to said horizontal magnets and operable sequentially, each ofsaid relays being operable to prevent reoperation of an associated oneof said horizontal magnets when the interconnection established by saidassociated one of said horizontal magnets is released.
 5. A display lampcontrol circuit in accordance with claim 4, further comprising meansresponsive to the release of the interconnection established by the lastoperable one of said horizontal magnets for releasing all of saidplurality of relays.
 6. A sequential control circuit comprising aplurality of lines capable of exhibiting service requests, a coordinateswitching array having a plurality of horizontal paths and a number ofvertical paths equal to the number of said lines, each of said verticalpaths corresponding to a particular one of said lines, means forestablishing a crosspoint connection in said array between one of saidhorizontal paths and the vertical path corresponding to aservice-requesting one of said lines for each of said lines in theservice-requesting condition, a service request display means associatedwith each of said lines, said display means having its operating pathprepared by a crosspoint connection between its corresponding verticalpath and a sequentially selected one of said horizontal paths, meanscontrolled by the crosspoint connection established to the first of saidsequentially selected horizontal paths for completing the operating pathfor one of said display means, and means controlled by the release ofsaid last-mentioned crosspoint connection for completing the displaydevice operating path prepared by the next sequentially selected one ofsaid horizontal paths.
 7. A telephone call allotter circuit comprising aplurality of telephone lines each having a line lamp associatedtherewith; a line relay associated with each of said lines, said relaybeing operable in response to the arrival of a call over a respectiveone of said lines; a coordinate switching array having a number ofhorizontal paths equal to the maximum number of calls desired to be heldwithout being answered and a number of vertical conductor paths equal tothe number of said telephone lines; means responsive to the operation ofeach of said line relays for selecting one of said horizontal pathsdependent upon the number of said horizontal paths which have previouslybeen selected; means for completing a crosspoint connection in saidarray at the intersection of said selected one of said horizontal pathswith the one of said vertical paths corresponding to said respective oneof said lines, each said crosspoint connection being effective toprepare an operating path to the line lamp associated with a respectivecalling one of said plurality of lines; and means responsive to therelease of one of said line relays for completing one of said preparedline lamp operating paths.